Ensure scope column of oauth_access_grants is not null

As of Doorkeeper 5.2.0.rc3, an authorization request must
include a 'scope' param in case the server does not define a
default scope, in line with https://tools.ietf.org/html/rfc6749#section-3.3.

https://github.com/doorkeeper-gem/doorkeeper/wiki/Migration-from-old-versions#from-51x-to-52x

db/migrate/20200220161244_change_scope_to_not_be_null_on_oauth_access_grants.rb

@@ -0,0 +1,13 @@
+class ChangeScopeToNotBeNullOnOauthAccessGrants < ActiveRecord::Migration[5.2]
+  def up
+    change_column_default :oauth_access_grants, :scopes, from: nil, to: ''
+    change_column_null :oauth_access_grants, :scopes, false
+  end
+
+  def down
+    change_column_default :oauth_access_grants, :scopes, from: '', to: nil
+    change_column_null :oauth_access_grants, :scopes, true
+  end
+end
+
+

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_09_03_120837) do
+ActiveRecord::Schema.define(version: 2020_02_20_161244) do
 
   create_table "batch_invitation_application_permissions", id: :integer, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8", force: :cascade do |t|
     t.integer "batch_invitation_id", null: false
@@ -94,7 +94,7 @@
     t.string "redirect_uri", null: false
     t.datetime "created_at", null: false
     t.datetime "revoked_at"
-    t.string "scopes"
+    t.string "scopes", default: "", null: false
     t.index ["token"], name: "index_oauth_access_grants_on_token", unique: true
   end